The present invention relates to a golf club head which can improve a directionality of a hit ball.
A golf club head is designed such that an accurate distance and directionality can be obtained by hitting a ball by a sweet spot of a face surface. However, actually, it is hard to expect that the ball is accurately hit by the sweet spot by a lot of average golfers except a professional golfer and some seniors, and the golfers having the skill mentioned above generally hit the ball at a position displaced to a toe side or a heel side from the sweet spot of the face surface. In this case, the head generates a micro rotational motion around a gravity point, and a side spin in an inverse direction to the rotational direction of the head is generated in the ball which is in contact with the face surface due to a frictional force. Accordingly, the hit ball is curved to an unintended direction. The operation mentioned above has been known as a gear effect.
Conventionally, in order to improve the directionality of the hit ball, there has been proposed increasing a moment of inertia of the head. The head mentioned above can make the rotational motion mentioned above of the head small even in the case that the ball is hit at the position which is displaced to the toe side or the heel side from the sweet spot of the face surface. For example, in Japanese published application 2003-245382 and Japanese published application H11-4919, there is described a matter that a moment of inertia is increased by employing a low specific gravity material such as a fiber reinforced resin in a part of the head.
The head having a large moment of inertia suppresses deterioration of the directionality, by inhibiting the rotational motion of the head with respect to a miss hit as mentioned above. However, as a state at the time of hitting the ball is shown in time sequence in FIGS. 12A to 12C, a face surface c of a head a tends to be open at the time of hitting a ball b (the face surface c is in a rightward directed state in the case of a right-handed golfer, and so forth). In the ball hit mentioned above, even if the ball b can be hit by the sweet spot of the face surface b, the ball b can not be hit in an intended direction.
A golf swing generally includes an address motion of coming to the ready while adapting the face surface c to a right direction, a take-back motion of swinging the club upward to the highest position (a top position) and a downswing motion of swinging the club downward from the top position. Since the face surface c generally becomes in an open state with respect to a target fly line direction A at the top position, it is necessary to execute a correction motion of turning back the head a to the face surface c so that the open is returned to the correct direction in the address state during the down swing motion from the top position to an impact, in order to correctly hit the ball. Accordingly, the correcting motion is hard to be effectively applied to the head having the great moment of inertia due to the great moment of inertia. As a result, it is considered that the head hits the ball b while the face surface c is kept open.